The applicant has developed a passenger protection device (hereinafter, simply referred to as air belt apparatus) in which when vehicle collision occurs an air bag accommodated in a shoulder belt of a seat belt expands concentratedly from the chest to an upper portion of the shoulder when a vehicle collision occurs, and which allows use of one product to handle two types of accident such as a frontal collision and a lateral collision (Takata Corporation, “Takata, Manufacturer of Safety System for Vehicle Exhibited Air Belt in GOOD DESIGN EXPOSITION 2011,” Aug. 24, 2011, searched on Dec. 15, 2011 via the internet <http://www.takata.com/pdf/110824_IP.pdf>).
In the air belt apparatus, the air bag expands in a substantial spindle shape along a shoulder belt fastened by a passenger. When the frontal collision occurs, the air bag inside the belt directly expands so that an area of the air bag that comes into contact with the chest of the passenger is widened, thereby dispersing and cushioning a shock to the chest. When the lateral collision occurs, an expansion portion holds the range from the upper portion of the chest to the temporal region of the passenger so as to control an amount of lateral movement of the head, thereby preventing a secondary collision against a side window or any structure inside a vehicle.
However, the air belt apparatus is equipped with two retractors, a retractor interposing a tong fixed to the seat belt so as to wind a lap belt and a retractor for winding the shoulder belt in which the air bag is accommodated as an air belt, thereby resulting in a high cost in manufacturing of the apparatus and resulting equipped only in a luxury vehicle.
In contrast, the development of an air belt apparatus is in progress allowing one retractor to pull out and wind the shoulder belt having the air belt built therein and the lap belt interposing a tong plate therebetween. Incidentally, in a case of utilizing one retractor, when webbing is pulled out of the retractor, the air belt portion needs to be able to smoothly slide with respect to the webbing so as to pull out a predetermined amount of the lap belt portion, and to cause the air belt portion (portion of shoulder belt) having the tong provided with the tong plate and a gas supply port at an end portion thereof to be located in an appropriate position from the chest to the shoulder.
Japanese Patent Application Publication No. 2009-029355 A discloses a seat belt apparatus having a flat tube which is made of a synthetic resin and is interposed between an air bag main body and the webbing. Japanese Patent Application Publication No. 2009-029355 A discloses various tubes of which rigidity (in longitudinal direction and width direction of tube) is adjusted in varying manners in order to reduce sliding friction of the webbing which is inserted into the flat tube and to ensure followability and flexibility when pulling out the webbing.